The subject matter of the invention relates to the technical field of visualizing and locating an anatomic structure or concrement in the body of a mammal, a human being in particular.
The locating and visualization of anatomic structures or concrements generally designated as targets in the remainder of the description, are currently performed using imaging devices based on different methods such as echography methods using ultrasound, or tomography methods based on X-rays, or on magnetic resonance (MRI). These imaging devices therefore allow the positioning of a therapeutic treatment system in relation to the target for treatment thereof by focusing shock waves or ultrasound waves on a focal point.
In the state of the art, a treatment apparatus is known from document DE 10 2006 060070, which comprises a system for treatment with acoustic pressure waves, using an imaging system of X-ray type, even if said document provides for the possible use of an imaging system of acoustic type. Said X-ray imaging system is mounted on a carrier structure that is mobile relative to the frame of the apparatus. Said apparatus also comprises a remote locating system allowing detection of the position of the treatment system and imaging system. The apparatus comprises a display screen on which the focal point of the treatment system and the target to be treated are visualized. The treatment system is moved to cause the focal point and the target to be treated to coincide.
Along the same lines, document DE 10 2004 006021 similarly describes a treatment apparatus in which there is no mechanical link between the imaging system, the therapy system and the table supporting the patient. This document describes a technique which, by means of the X-ray imaging system, is used to align the focal point of the therapy system with the target to be treated. The document teaches taking a series of X-ray pictures from two angles and identifying in each of the pictures the iso-centre of the imaging system, the focal point of the therapy system and the target, then of causing the focal point and the target to coincide by moving either one thereof, bearing in mind that all the degrees of freedom associated with these movements are provided with encoders allowing determination of values of movement.
It is to be noted that the physical principle of image projection by an imaging system of X-ray type allows visual tracking of the alignment of the target and focal point, since this imaging system is permanently oriented to monitor the volume located around the focal point. However, in general, imaging systems of X-ray type are costly, complex and cumbersome which means that it appears difficult to use these in combination with treatment systems. Also, the monitoring of the alignment of the target and focal point using X-rays requires continuous irradiation of the patient, which is harmful for the patient and nursing staff.
Ultrasound systems, on the other hand, are more compact, less costly and can easily be used in combination with therapeutic treatment systems. In addition, contrary to X-ray devices, ultrasound systems do not emit any ionizing radiation.
In the state of the art, there are numerous embodiments of apparatus which combine an ultrasound probe of an imaging system with a treatment system focusing waves on a focal point. In general, the locating device allows the target to be treated and the focal point of the treatment apparatus to be visualized in the image. Causing the target to coincide with the focal point is obtained by moving either the focal point of the treatment system, or the target i.e. the table supporting the patient. This coinciding evidently requires knowledge of the orientation of the image plane in relation to the axes of mechanical movement of the table or treatment apparatus. By measuring the coordinates of the target and focal point in the image, and from knowledge of the orientation of the image plane, it is possible to calculate the distance separating the target and the focal point and to move the focal point, namely the treatment device or the target, to cause them to coincide.
In the state of the art, it is known, notably from EP 0 404 871 or U.S. Pat. No. 5,078,124, to position the ultrasound probe of the imaging system so that it permanently targets the focal point of the treatment apparatus and so that this focal point continually appears in the image. The axis of the image plane passes through the focal point of the therapy apparatus. To cause the target to appear on the same image plane, the operator can either move the patient so that the image of the target appears in the ultrasound image, or move the ultrasound probe about its axis targeting the focal point until the target appears in the ultrasound image.
It is to be considered that the ultrasound probe is always joined to a mechanical holder targeting the focal point of the treatment apparatus. This constraint is extremely penalising for the operator, insofar as it appears difficult in some cases to find the target having regard to the limited movements of the probe and/or patient to obtain the target and focal point in one same image. Also, it appears difficult to adjust the plane of the ultrasound image slice relative to the anatomy of the observed target to obtain the best possible definition of the contours or inner side of the target.
It is to be noted that U.S. Pat. No. 5,944,663 describes a treatment method comprising a focused ultrasound source which is not combined with an imaging device. Imaging of the patient is performed during a phase prior to the treatment phase. This method provides for causing the marking of the imaging device to coincide with the marking of the therapy device. This coinciding is achieved through the presence of markers positioned on the table supporting the patient, and which are visualized by the locating system during each of the imaging then therapy phases. The images of the patient are positioned in relation to the table markers which are identified in marking associated with the imaging device. These same markers are then positioned in the marking associated with the therapy device. The therapy probe is positioned within this same marking by means of a second set of markers joined to the therapy device. Therefore, with said method it is possible, within one same reference marking, to arrange the entire dataset required to cause patient imaging to coincide with the treatment region, in order to display the position of the focal point in the image volume.
The main drawback with this technique concerns the fact that imaging is not carried out in real time, since imaging is conducted during a phase prior to the treatment phase. This technique does not allow monitoring and confirmation of the correct positioning of the therapy device in relation to the targeted region. This approach is based on full immobility of the patient during the treatment phase, which appears difficult to implement in practice.